1. Field of the Invention
The present invention relates in the field of wound dressings. More specifically, the present invention is directed to a process for controlling the absorbency and other physical properties of collagen flakes, particles, or powders used for medium to highly exudative wounds.
2. Description of Related Art
Older Americans make up the largest group of persons developing chronic wounds such as pressure ulcers. In 1992, the number of persons 65 years or older in the U.S. numbered 32.3 million or 12.7 percent of the population. By 2030, it is estimated the number will approach 70 million, 20 percent of the population (Toth 1995 xe2x80x9cCost-Effective Pressure Ulcer Management in Extended Care,xe2x80x9d Ostomy/Wound Management Vol. 41 No. 7A August 1995). The wound care market has made much progress in regards to the durability and ability to expedite healing over many traditional products. Many efforts have been made to produce products with the increased durability and absorption capabilities. With the recent developments made in collagen, collagen dressings are preferred because of their superior healing properties.
There is an existing market of powdered wound dressings/fillers for the treatment of medium to highly exudative wounds. Examples of commercially available synthetic surgical powder dressings include those sold under the trade names: COMFEEL ULCUS (Colorplast, Denmark), DUODERM (Convatec, UK), HyCURE (SouthWest Technologies Inc., USA), and MEDIFIL (Biocore Medical Technologies, Inc. USA).
Accordingly, a number of attempts have been made to improve the use of collagen flakes in wound healing applications.
U.S. Pat. No. 6,136,341 (Petito) discloses a method and composition used to promote healing wherein the composition is in the form of a powder and has a moisture content of approximately 4 to 7% and a pH range from 5.5 to 6.5. The powder is used on wounds with a large amount of exudate.
U.S. Pat. No. 5,836,970 (Pandit) discloses a composite powder of maltodextrin/chitosan salt alginate with some collagen that provides an absorption capacity for wound healing applications.
U.S. Pat. No. 4,952,618 (Olsen) discloses a hydrocolloid adhesive composition for use as a wound dressing having polycationic and polyanionic hydrocolloid particles made of chitosan salt used to provide an increased integrity of the hydrocolloid particle without a decrease of absorbency.
In U.S. Pat. No. 5,196,185 (Silver et al), the inventor discusses that the use of wound dressings comprised of Type I collagen have had limited commercial success because of the difficulty of the physical form of the dressing. Collagen in the particulate form adheres well to wounds because of its high surface areas but is difficult to apply as dry powder because of its high surface charge.
The properties of collagen flakes that are important in wound care applications include absorbency, porosity, density and color (for cosmetic purposes). These properties are important as the dressings are designed to maintain a moist wound environment. For highly exudative wounds, a high absorbency is desired. For wounds with minimal or moderate exudate, it is important that the product not have high absorption abilities to ensure a moist environment.
There are methods available for the production of collagen flakes in prior art literature. The relevance of absorbency also suggests that it is an important implication for the ability of different products to cope with fluid production. None of the prior art literature provides a method for controlling and adjusting the absorbency and porosity of collagen flakes to suit the needs of the user in wound healing. Therefore, a need exists for a method for controlling the properties of collagen flakes, powder, and particles in wound healing applications.
The present invention provides an absorbent wound dressing that will maintain a moist environment at the wound interface and provide a barrier to microorganisms. The dressing should also provide conformability to the wound surface, vapor/gas permeability, be non-adherent and easily removed without causing additional trauma. The collagen powder (which forms a gel as it absorbs exudate) creates a moist environment that when combined with a secondary covering forms an occlusive dressing over the wound site for the treatment of stage II to IV wounds.
The present invention also provides a method for controlling the absorbency of the collagen powder product.
The present invention further provides a method for controlling the density of the collagen powder product.
The present invention further provides a method for controlling the porosity of the collagen powder product.
The present invention further provides a method for controlling the color of the collagen powder product.
The present invention further provides a wound dressing that uses collagen as its starting material.
The present invention also provides for a collagen powder material that is biocompatible.
The present invention provides for a collagen material that can be used as a collagen powder wherein the improvement of the collagen powder is in terms of its porosity, absorbency, density and color.
The terms xe2x80x9cflakes,xe2x80x9d xe2x80x9cparticles,xe2x80x9d and xe2x80x9cpowdersxe2x80x9d have been loosely defined and used in various literature to indicate a wound product that is in the form of a finely divided solid usually less than 2 mm in dimension.
Natural insoluble collagen, as defined in U.S. Pat. No. 4,925,924 (Silver et al), and incorporated by reference herein, refers to collagen that cannot be dissolved in an aqueous acidic or alkaline or in any inorganic salt solution without chemical modification and includes hides, splits, and other mammalian or reptilian coverings.
More particularly, natural insoluble collagen refers to the corium, which is the intermediate layer of a bovine hide between the grain and the flesh sides. Collagen constitutes the connective tissue and is the major type of fibrous protein in higher vertebrae. Collagen in its natural state exists in a triple chain helix along with constant periodicity between aligned triple chains. Collagen stimulates angiogenesis, fibroporesis and epidermal growth. The starting material for the present invention is a collagen suspension derived from any of the above sources.
The process of manufacturing collagen products as referred in U.S. Pat. No. 4,925,924, and thus incorporated by reference therein, discloses using collagen as the starting material. It also discloses dispersing an inorganic acid such as hydrochloric acid into a collagen suspension. The collagen suspension has a concentration of about 0.5 to about 1% weight volume. The temperatures at which dispersions are freeze-dried at a product temperature range from about xe2x88x9220xc2x0 C. to about xe2x88x9235xc2x0 C., preferably at about xe2x88x9230xc2x0 C. The dispersing or blending is performed with any suitable mechanical blending means.
The collagen dispersion is deaerated under appropriate vacuum, which has a pressure of less than 0.4 millitorr. The collagen dispersion is then frozen under optimum conditions to obtain a fibrous structure containing numerous pores. When it is desired to have a crosslinked product, the crosslinking can be performed by any method known in the art. The crosslinking as described in U.S. Pat. No. 4,925,924 results in a crosslinked sponge product with stable pores and channels, having dual porosity.
In alternate prior art methods, collagen suspensions may have concentrations of up to 7% weight volume. These suspensions are frozen in trays and freeze-dried at product temperature ranges of about xe2x88x9240xc2x0 C. to about xe2x88x9210xc2x0 C. Freeze-drying, like all drying processes, is a method to separate liquid water from a wet solid product, or from a solution or dispersion of given concentration. The main difference is that the liquid water is separated by solidification (i.e. the formation of ice crystals) and subsequent vacuum sublimation instead of evaporation. This allows drying at subzero temperatures which can be advantageous in the case of heat sensitive-products. Collagen flakes are produced when the collagen sponges obtained after freeze-drying, are ground to a suitable size.
Any of the size reduction processes and equipment such as shredders, rotary cutters and dicers, peripheral speed mills and fluid energy superline mills may be used. The process of obtaining collagen flakes as described above is known. The collagen flakes thus obtained are usually white in color, have a high absorbency (of 20 to 40 times), high porosity and light density.
The present invention is illustrated by the following examples contained in the detailed preferred embodiments of the invention. The present disclosure is exemplary of the principles of the invention and is not intended to limit the invention to the embodiments illustrated and described.
In the preferred embodiment, the properties of collagen flakes thus obtained, using prior art methods disclosed above, are improved using the process described below. The properties of collagen flakes are modified by subjecting the flakes to temperatures exceeding 80xc2x0 C. over varying durations of time. In the preferred embodiment, the freeze-dried collagen flakes are spread over a tray in a compartment type dryer. The flakes may be spread over a tier of trays. Heating is performed by direct contact with a gas such as hydrogen, at a higher temperature, which may be directed parallel or perpendicular to the tray.
In another embodiment of the present invention, the collagen flakes may be heated indirectly by the use of heated shelves, radiation coils or refractory walls inside the housing. The temperature to which the collagen flakes are heated may vary with the length of time used to achieve the desired results.
Generally, lesser amounts of time are required for higher temperatures, to achieve similar results. For instance, collagen flakes which are subjected to a temperature of 140xc2x0 C. for 180 minutes contained physical properties similar to collagen flakes subjected to 150xc2x0 C. for 120 minutes. The properties of collagen flakes subjected to those operating conditions were found to be significantly different from the properties of starting collagen flakes. For example, collagen flakes subjected to a temperature of 180xc2x0 C. over 72 hours exhibited a decrease in both absorbency and porosity.
In yet another embodiment of the present invention, there is a described process of controlling the properties of collagen flakes, which includes heating freeze-dried collagen sponges to varying temperatures at various periods of time prior to size reduction.